Method of inhibiting metal corrosion by amine-stabilized unsaturated chlorinated hydrocarbons



United States Patent METHOD 0F INHEBITING WETAL CORROSION BY AMINE-STABILIZED UNSATURATED CHLG- REIATED HYDROCARBONS (USING SUBSTI- TUTED OXERANES) Wilbur H. Petering and Wiliiam A. Caliahan, Detroit, Mich, assignors to Detrex Chemical Industries, Inc., Detroit, Mich, a corporation of Michigan No Drawing. Original application July 23, 1954, Ser. No. 445,474. Divided and this application May 5, 1960, Ser. No. 26,942

14 Claims. (Ci. 252-453) This a divisional application of our co-pending US. application Serial No. 445,474, filed July 23, 1954, and now abandoned.

This invention relates to a method of inhibiting the tarring and corrosion of certain metals such as iron or copper in the liquid phase of hot, dry amine-stabilized, unsaturated chlorinated hydrocarbons. Among the unsaturated chlorinated hydrocarbons to which the method of the present invention is applicable are trichlorethylene and perchlorethylene.

It is conventional in the art to add stabilizers of various types to chlorinated hydrocarbons. Among the accepted stabilizers are the phenolic compounds, amines, and various azo compounds. However, the choice of such compounds is quite limited except in the case of a few of the higher boiling chlorinated hydrocarbons, since most of the stabilizers also have relatively high boiling points. A wide difference in boiling points between the solvent and the stabilizers is undesirable because of the difficulty of stabilizing the vapor phase, and it is therefore desirable to provide a combination of a solvent and stabilizers not having wide differences in boiling points. Moreover, the distillation of the solvent may otherwise result in a complete loss of the stabilizer either in production or in subsequent use.

The organic amine bases have enjoyed widespread use as stabilizers for unsaturated chlorinated hydrocarbons. Such bases, including aliphatic amines and basic cyclic compounds characterized by nitrogen in the ring such as pyridine and the like are disclosed in the patents to Dinley, numbers 2,096,735, 2,096,736 and 2,096,737. Under many conditions the volatile aliphatic amine and/ or heterocyclic nitrogen bases disclosed in the Dinley patents are highly effective and desirable stabilizers for chlorinated hydrocarbons. However, these stabilizers, as disclosed by Dinley, must boil fairly close to the solvent stabilized to have any real utility.

In the manufacture of unsaturated chlorinated hydrocarbons such as trichlorethylene, for example, the recovery of a neutral, sweet, relatively pure product is almost impossible Without the use of a stabilizer such as amines. The amine stabilizer should be present in the refining operation, as distinguished from adding amine to the refined product, and the amine should be volatile with the chlorinated hydrocarbon and therefore carry over from the refining operation into the refined product. Unless a neutral, sweet product is obtained when the solvent is refined, subsequent attempts to stabilize the solvent often prove futile, or at least extremely costly and time consuming. Thus, the amines are not only highly effective and desirable stabilizers, but their use in both the liquid and vapor in the last stages of manufacture is almost essential.

Yet, in spite of the effectiveness and desirability of the amines as stabliziers, there appears to be an undesirable reaction or set of reactions which take place when the amines are used as stabilizers in unsaturated chlorinated hydrocarbon solvents in the presence of certain metals such as iron or copper or their alloys. It has now been discovered that the lower boiling unsaturated chlorinated hydrocarbons, when stabilized with certain of the conventional organic amines, such amines having boiling points not widely different from the boiling points of the chlorinated hydrocarbons, appear to enter into a complex reaction when exposed to these metals, with resulting tarring and corrosion of the exposed metal surfaces.

The tarring and corrosive action of the amine-chlorinated hydrocarbon system appears to be related to certain specific metals, especially iron (also in its common alloyed forms) and copper (alone or in its alloyed forms). Aluminum on the other hand, which is known to be an agent for metal induced decomposition in some cases, does not initiate the tarring and corrosion reaction in aminestabilized systems.

In referring to amines in the foregoing paragraph we have used the term in its broad sense. The other organic bases specified in the Dinley patents, including cyclic compounds characterized by nitrogen in the ring, such as pyridine and morpholine, for example, are included within the meaning of this term. Among the suitable amines are pyridine, di sec butylamine, diisopropylamine, diethylamine, n-butylamine, amylamines, methyl pyridines, N- methyl morpholine, triethylamine, and hexylamines.

The exact mechanism by which the amine reacts with the chlorinated hydrocarbon in the presence of the metal is not completely known or understood. It may be that the amine, being a base, either forms a covalent bond with one carbon atom of the unsaturated chlorinated hydrocarbon, and the resulting fragment reacts with the metal; or, in the case of chlorinated hydrocarbons containing hydrogen, the amine may react by first removing a hydrogen to yield ionic fragments which in turn are reactive toward metalsthe end products of such reactions being more or less complex metal organic chlorocompounds. Then again, the metal may be the initiator of the set of reactions which involve the amine and the chlorinated solvent.

Regardless of what th true explanation of the phenomenon may be, serious tarring and corrosion problems are encountered when an unsaturated chlorinated hydrocarbon is stabilized with an amine and the product exposed to a ferrous or cuprous metal, particularly when the hydrocarbon is hot and bone-dry.

It is accordingly an object of this invention to provide a method for overcoming the foregoing disadvantages, thereby providing an improved tarring and corrosion inhibiting stabilizer composition for the lower boiling unsaturated chlorinated hydrocarbons. Other objects and advantages of this invention will further appear hereinafter.

In accordance with this invention, the tarring and corrosive action of the organic amine in the presence of certain metals and the chlorinated hydrocarbon is in hibited by incorporating into the mixture a small amount of an oxygen-containing compound. The oxygen compound does not interfere with the stabilizing action of the amine, or its ability to act as an alkaline material or to act as a reducing agent. The oxygen-containing compounds utilized in accordance with the method of this invention are epoxy compounds. It appears that these oxygen compounds may act to retard or interfere with the tarring and corrosive activity of the amine-chlorinated hydrocarbon system either by blocking the tarring and corrosive activity of the amine-stabiliezd system or by forming a protective layer over the surface of the metal. In the former case the amount of oxygen compound required to control the action of the amine would be related to the amount of amine used, while in the latter case the amount of oxygen compound required would be related to the surface area of the metal exposed to the solvent and amine. The amount of oxygen compound required seems to be related to the amount of amine.

It has been found that metal tarring and corrosion which occurs in the amine-chlorinated solvent-metal system containing only the usual stabilizing amount of amine can be reduced by using much larger quantities of amine. This larger quantity of amine may be of the order of ten times the usual stabilizing amount. It is believed that these very large quantities of amine may form a protective coating on the metal surface, thus interfering with the reaction between the amine, the chlorinated solvent and the metal. This method of controlling the tarring and corrosion of the metal is not desirable because the normal gradual reduction in amine content during use will bring the amine concentration into the range where the tarring and corrosion of the metal will rapidly increase and the difficulties described above be encountered; moreover, the use of such large amounts of amine greatly increase solvent stabilization costs and may introduce highly objectionable odors into solvent.

The epoxy compounds which are useful in accordance with the method of this invention are organic compounds having the linkage The following epoxy compounds are illustrative of' (2) Butylene oxides 4 (3) Cyclohexene oxide In accordance with this invention the crude unsaturated chlorinated hydrocarbon, prior to the refining operation, may be combined with a stabilizing proportion of amine. The stabilized product is combined with an inhibitive proportion of an epoxy compound. The epoxy compound is chosen so that it has a boiling point slightly higher than that of the amine-stabilized chlorinated hydrocarbon being refined. This results in higher concentrations of the epoxy compound in the liquid phase than in the vapor phase and in an inhibition of the metal tarring and corrosion which would otherwise occur in the hot anhydrous amine-stabilized solvent in the bottom of the still during distillation. The amine, and not the epoxide, stabilizes the chlorinated solvent.

Unsaturated chlorinated hydrocarbons such as trichlorethylene and perchlorethylene are widely used as degreasing solvents, cleaners and the like. For example, ferrous metals are degreased commercially by subjecting them to the liquid and vapor phases of chlorinated hydrocarbons. When the chlorinated hydrocarbon is hot, dry and amine-stabilized, there is some danger of tarring and corrosion of the degreasing apparatus or of metal immersed in the liquid. Accordingly, it is commercially advantageous to provide a chlorinated hydrocarbon solvent which contains both an amine and an oxygen compound in accordance with the method of this invention.

It is well known in the art that the proportions of amine stabilizers may vary from trace values (such as .01% by weight or less) to as high as 1.0% by weight, based on the weight of the chlorinated hydrocarbon. However, a range of the order of about .O2.20% by weight represents the proportions considered commercially preferable in most amine-stabilized chlorinated hydrocarbons. Amine stabilizers have been well known and extensively used, and different amines have been used in various proportions for individual chlorinated hydrocarbons. The art is well aware of the proper concentration of each specific amine stabilizer in each specific chlorinated hydrocarbon, and such concentrations are conveniently referred to as stabilizing amounts and are so defined herein.

The concentration of the oxygen-containing compound may be varied from about .01% by weight to about 5% by weight, but a range of about .0ll.0% by weight is preferred. Such concentrations are referred to as inhibitive amounts, and are so defined herein. Preferably the quantity of oxygen-containing compound is about 1-5 times the quantity of amine stabilizer.

The corrosion and tarring inhibiting effects of the addition of the oxygen compounds of the present invention may readily be shown by simple tests. These tests involve periods of refluxing of solvent samples with weighed ferrous or cuprous strips partially immersed in the liquid phase of the solvent. A group of tests is run to compare the effects of various systems. A typical group would consist of the following samples:

(a) Solvent and metal strip (b) Amine-stabilized solvent and metal strip (c) Amine-stabilized solvent, oxygen compound and metal strip (d) Solvent, oxygen compound and metal strip.

The typical results of each of these tests may be summarized as follows:

Test (a): The metal strip was in good condition after reflux, showing very little or no corrosion or tarring.

The solvent showed definite signs of breakdown as would be expected.

Test (b): The metal strip showed considerable tarring and corrosion after reflux. While the degree of tarring TABLE HA and corrosion varied somewhat with diflerent amines the characteristic tarring and corrosion by amine-stabilized solvent was always apparent. The solvent showed varying degrees of breakdown from none to considerable,

Corrosive Efiect of Various Amines on Steel in T richlorethylene and the Inhibitory Efiect of an Epoxide 0r Oxriane (Epichlorhydrin) depending on the length of the test and the amine chosen.

Test (c): The metal strip showed dramatically re- A lzercent oXirane, Fgollrs 114ml Extent of duced tarring and corrosion. The solvent showed varymme & 0 test fia; tamng ing degrees of breakdown from almost none to considerable, depending on the length of the test and the amine 0. 02 None 134.5 1, 917 Severe. chosen Do 0. 02 0. 10 134. 5 17s Slight.

r D0 0.20 None 134.5 10, 800 Very Test (d): The metal strip was in good condition arter severe reflux, showing very little or no corrosion or tarring. The BM 58 gf solvents showed definite signs of breakdown. Comzn i igziel 0. 02 None 8- 1,835 Severe- Il e. The results of reflux tests of the type described with varip Q02 14M 47 fi ht A 81g ous combinations of StablhZvI'S and inhibitors are given 20 Diisopropylamine M2 None 1650 110 Slight. in Tables IA and IB. Do o. 02 0.10 165.0 5 None. Do 0. 20 None 165. 0 72 Slight Do. 0. 20 0.10 165. 0 10 None Amylarnine 0. 02 None 165. 0 1, 100 Severe TABLE 1A Do 0. 20 None 165.0 8,100 Very SGVGIG T W h T 1 h l M iii i 'ri '33 ri ii 1 gnght R W 1,; it [C1 e y pyri ine 0. one 8.0 ,26 evere efl 1: es r lore! y ene Do 0.02 0.10 148.0 43 Vegyht s g N -n1ethhyl1m 0. 02 None 62. O 2, 260 Severe. Metal Amine Oxirane Corrision Tarring %g 02 10 0 596 M Odcmte Refined triethyl- 0. 02 None 124.5 1,619 Severe.

amine. g g jk a 30 C Do 1 0. 2 2 gone 154 3 78 7 l t doderate. ominercia 0. a one ,80 ery Steel very gg triethylamine. severe. Copper do go 02 10 3 II 8 SNone.

o.-. .02 one eavy evere. Steel Bad Heavy- 130-- 0. 02 0. 05 116.0 0 None.

Do 0. 02 0.10 116. 0 0 Do. None None 0.10 165.0 10 Do. Copper do o Do. teel Bntyene Slight Slight.

0X1 600 A similar series of tests was run in which perchlorethylfggg ene was substituted for trichlorethylene. The results of oxide 112 none, these tests are shown in Table IIB: gpichlorlgy 4:0

rin 0.0 Copier i5 do do "g" i] .do L 50. TABLE HB te 'iso 0 l Pent e Shtt tto 8 m; Dy on e 5 .1 lrgnedium Corrosive Efiect of Venous Amines on Steel Strip in Per- 2 g do g- Do chlorethylene and the Inhibitory Effect of an Epoxide 'ifininyi n'in'e 'iifii ine "very Very r Oxirane p y 0.02%. oxide 0.10% slight slight. Copper do .d0 ight- Slight.

Percent Oxirane, Hours Metal Extent of Amino by percent of loss, tarriug weight by Wt. test rngrrn/ft. TABLE 1B Hexylarnine 0.02 None 136 274 Moderate. D 0. 02 0.10 136 5 None. Reflux Tests With Perchlorethylene 0220 Nofle 136 570 Moderate- Disecbutylamine. 0. 02 None 63 1, 208 Severe.

o 0. 02 0. 1o 63 43 None. Refined rnorpholine. 0. Noilig 253 1Sight. Do 0. 0. one. Metal Amine OXirane COTI'OSIOH Tarring r 5 Do 0 20 None 605 Severe O oomme o i 0. 02 None as 1, 185 Do.

morp 0 me. i..?i fifii ho. g M2 None 72 585 M N-rneth .do Very mom 0 D 0. 10 None 72 668 Do. mg'rggme heavy 02 N 05 12 sli iit' Copper do do Heavy. one g Steel do Diisobiitylene Slight. Q05 72 None oxide 005%. 0. 02 0. 10 120 5 D0. Copper do 0. 20 None 120 348 Moderate Steel .do Epiehlorhy- Very Very Q20 120 9 None drin 002% slight Slight 0.02 None 16 Heavy Severe cyclohexene 0. 02 0. 05 96 None None. 0 3% 0.02 0.05 144 do. Do. Copper "do do DO 0. 02 0.10 144 None Do. Steel .do Epichlorhy- Do. 87

him 3% None 0.10 87 H. o Do. Copper do .do Do.

In order to show the corrosive eflects of amine-stabilized solvent on metal and the inhibitory effects of epoxides or substituted oxiranes, a series of reflux tests were run in which various amines were used while the metal (steel), the oxirane (epichlorhydrin), and the solvent 75 tarring and corrosion in the reboiler are obtained With the use of an epoxy compound boiling slightly higher than the amine-stabilized solvent.

When a chlorinated solvent is used in degreasing, particularly vapor degreasing, the amine-stabilized solvent is heated in the boil sump. The amine-stabilized solvent vapors are, however, used to heat the work going into the degreaser. This results in the work being in contact with hot dry liquid amine-stabilized solvent. In this case best results are obtained if a combination of inhibitors is used. One inhibitor may be chosen to boil slightly below the amine stabilized solvent while the other may be chosen to boil slightly above the amine stabilized solvent.

The following examples will serve to show the best mode of accomplishing the above objectives:

EXAMPLE 1 Trichlorethylene: Percent Triethylamine 0.01 Butylene oxide 0.05

EXAMPLE 2 Trichlorethylene Triethylamine 0.01 Butylene oxide 0.03 Epichlorhydrin 0.02

EXAMPLE 3 Trichlorethylene:

Diisopropylamine 0.0125 Pentene oxide 0.05

EXAMPLE 4 Perchlorethylene I N-methyl morpholine 0.01 1,2-diisobutylene oxide 0.05

EXAMPLE 5 Perchlorethylene:

N-methylmorpholine 0.01 Epichlorhydrin 0.02 Cyclohexene oxide 0.03

EXAMPLE 6 Perchlorethylene:

N-methyl morpholine 0.01 Epichlorhydrin 0.03

In this specification and claims the terms epoxy and oxirane are used synonymously. The tests clearly show that the amine stabilizes the solvent while the epoxy compound does not. They also show that the presence of the amine results in tarring and corrosion while the addition of the epoxy compound to the amine-stabilized solvent results in a dramatic reduction of tarring and corrosion. The solvent alone or with the epoxy compound does not appreciably cause metal corrosion or tarring under the conditions of these tests. The epoxy compound does not stabilize the solvent, it has the unexpected result of inhibiting tarring and corrosion in an amine stabilized system.

Having thus described our invention, we claim:

1. In a process wherein a metal selected from the class consisting of ferrous and cuprous metals is exposed to a hot, dry, unsaturated low molecular Weight chlorinated hydrocarbon selected from the class consisting of trichlorethylene and perchlorethylene, and containing a stabilizing amount of a volatile organic nitrogen compound selected from the group consisting of aliphatic amines and heterocyclic nitrogen bases, said nitrogen compound stabilized chlorinated hydrocarbon normally causing tarring and corrosion of said metal, the improvement which comprises incorporating into said nitrogen compound stabilized chlorinated hydrocarbon about .015% by weight of an inhibitor for said metal tarring and corrosion comprisa substituted oxirane selected from the class consisting of epichlorhydrin, butylene oxide, pentene oxide, cyclohexene oxide and 1,2-diisobutylene oxide.

2. The process of claim 1 wherein said substituted oxirane has a boiling point higher than that of said stabilized solvent.

3. In a method of refining a crude volatile low molecular weight chlorinated unsaturated hydrocarbon solvent selected from the class consisting of triehlorethylene and perchlorethylene in the presence of a metal selected from the class consisting of ferrous and cuprous metals, said solvent having incorporated therein a stabilizing amount of a volatile organic nitrogen compound selected from the group consisting of aliphatic amines and hcterocyclic nitrogen oases, said nitrogen compound stabilized solvent normally causing tarring and corrosion of said metal, the improvement which comprises incorporating into said nitrogen compound stabilized chlorinated hydrocarbon about .01-5 by weight of an inhibitor for said metal tarring and corrosion comprising a substituted oxirane selected from the class consisting of epichlorhydrin, butylene oxide, pentene oxide, cyclohexene oxide and 1,2-diisobutylene oxide, wherein said substituted oxirane has a boiling point higher than that of the nitrogen compound stabilized chlorinated hydrocarbon.

4. In a process of degreasing metal surfaces selected from the class consisting of ferrous and cuprous metals with a hot, volatile, unsaturated chlorinated hydrocarbon selected from the class consisting of trichlorethylene and perchlorethylene, and containing a stabilizing amount of a volatile organic nitrogen compound selected from the group consisting of aliphatic amines and heterocyclic nitrogen bases, said nitrogen compound stabilized chlorinated hydrocarbon normally causing tarring and corrosion of said metal, the improvement which comprises incorporating into said nitrogen compound stabilized chlorinated hydrocarbon about .0l5% by weight of an inhibitor for said metal tarring and corrosion comprising a substituted oxirane selected from the class consisting of epichlorhydrin, butylene oxide, pentene oxide, cyclohexene oxide and 1,2-diisobutylene oxide.

5. In a process of degreasing metal surfaces selected from the class consisting of ferrous and cuprous metals with a hot, volatile, unsaturated chlorinated hydrocarbon selected from the group consisting of trichlorethylene and perchlorethylene, and containing a stabilizing amount of a volatile organic nitrogen compound selected from the group consisting of aliphatic amines and heteroeyclic nitrogen bases, said nitrogen compound stabilized chlorinated hydrocarbon normally causing tarring and corrosion of said metal, the improvement which comprises incorporating into said nitrogen compound stabilized chlorinated hydrocarbon about .0l5% by weight of a combination of at least two inhibitors for said metal tarring and corrosion, each of said inhibitors comprising a substituted oxirane selected from the class consisting of epichlorhydrin, butylene oxide, pentene oxide, cyclohexene oxide and 1,2-diisobutylene oxide, wherein at least one of said inhibitors has a boiling point higher than that of said nitrogen compound stabilized solvent, and at least one of said inhibitors has a boiling point lower than that of said nitrogen compound stabilized solvent.

6. The process of claim 5, wherein the substituted oxiranes are butylene oxide and epichlorhydrin.

7. The process of claim 5, wherein the substituted oxiranes are butylene oxide and cyclohexene oxide.

8. The process of claim 5, wherein the substituted oxiranes are pentene oxide and epichlorhydrin.

9. The process of claim 5, wherein the subsituted oxiranes are pentene oxide and cyclohexene oxide.

10. The process of claim 5, wherein the substituted oxiranes are pentene oxide and 1,2-diisobutylene oxide.

11. The process of claim 5, wherein the substituted oxiranes are epichlorhydrin and cyclohexene oxide.

12. The process of claim 5, wherein the substituted oxiranes are epichlorhydrin and 1,2-diisobutylene oxide.

13. In a process of degreasing objects having metal surfaces selected from the class consisting of ferrous and cuprous with a hot, volatile, unsaturated chlorinated hydrocarbon, said chlorinated hydrocarbon being selected from the group consisting of trichlorethylene and perchlorethylene, said chlorinated hydrocarbon having incorporated therein a stabilizing amount of a volatile organic nitrogen base selected from the group consisting of pyridine, di sec butylamine, diisopropylamine, diethyl amine, n-butylamine, amylamine, methyl pyridine, N-methyl morpholine, triethylamine and hexylamine, said nitrogen compound stabilized solvent normally causing tarring and corrosion of said metal surfaces, the improvement which comprises incorporating into said nitrogen compound stabilized chlorinated hydrocarbon about .01-5% by Weight of an inhibitor for said metal tarring and corrosion comprising a substituted oxirane selected from the class consisting of epichlorhydrin, butylene oxide, pentene oxide, cyclohexene oxide and 1,2-diisobutylene oxide, Wherein said substituted oxirane has a boiling point higher than 10 that of the nitrogen compound stabilized chlorinated hydrocarbon.

14. The process of claim 13 oxirane is epichlorhydrin.

wherein said substituted References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,133,885 May 19, 1964 Wilbur H. Petering et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected belo Column 3, line 61, for "componds" read compounds column 4, line 49, for "conveniently" read conventionally column 6, TABLE IIA, line 3 of the heading thereof, for Oxriane", in italics, read Oxirane in italics; column 7,. line 71, for. "compris" read comprising column 8, line 75, after "cuprous" insert metals Signed and sealed this 20th day of October 1964.

SEAL A ttest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. IN A PROCESS WHEREIN A METAL SELECTED FROM THE CLASS CONSISTING OFFERROUS AND CUPROUS METALS IS EXPOSED TO A HOT, DRY, UNSATRUATED LOW MOLECULAR WEIGHT CHLORINATED HYDROCARBON SELECTED FROM THE CLASS CONSISTING OF TRICHLORETHYLENE AND PERCHLORETHYLENE, AND CONTAINING A STABILIZING AMOUNT OF A VOLATILE ORGANIC NITROGEN COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC AMINES AND HETEROCYCLIC NITROGEN BASES, SAID NITROGEN COMPOUND STABILIZED CHLORINATED HYDROCARBON NORMALLY CAUSING TARRING AND CORROSION OF SAID METAL, THE IMPROVEMENT WHICH COMPRISES INCORPORATING INTO SAID NITROGEN COMPOUND STABILIZED CHLORINATED HYDROCARBON ABOUT .01-5% BY WEIGHT OF AN INHIBITOR FOR SAID METAL TARRING AND CORROSION COMPRISA SUBSTITUTED OXIRANE SELECTED FROM THE CLASS CONSISTING OF EPICHLORHYDRIN, BUTYLENE OXIDE, PENTENE OXIDE, CYCLOHEXENE OXIDE AND 1,2-DIISOBUTYLENE OXIDE. 